Polycrystalline diamond construction and method for making same

ABSTRACT

A polycrystalline diamond construction comprising a body of polycrystalline diamond material is formed of a mass of diamond grains exhibiting inter-granular bonding and defining a plurality of interstitial regions therebetween, and a non-diamond phase at least partially filling a plurality of the interstitial regions to form non-diamond phase pools, the non-diamond phase pools each having an individual cross-sectional area. The percentage of non-diamond phase in the total area of a cross-section of the body of polycrystalline diamond material and the mean of the individual cross-sectional areas of the non-diamond phase pools in the image analysed using an image analysis technique at a selected magnification is less than 0.7, or less than 0.340 microns squared, or between around 0.005 to 0.340 microns squared depending on the percentage of non-diamond phase in the total area of the cross-section of the polycrystalline diamond construction. There is also disclosed a method of making such a construction.

FIELD

This disclosure relates to a polycrystalline diamond construction formedof polycrystalline diamond (PCD) material, a method for making the sameand tools comprising same, particularly but not exclusively for use inboring into the earth.

BACKGROUND

Polycrystalline diamond (PCD) material comprises a mass of inter-bondeddiamond grains and interstices between the diamond grains. A body of PCDmaterial may be made by subjecting an aggregated mass of diamond grainsto a high pressure and temperature in the presence of a sintering aidwhich is typically a metal such as cobalt, nickel, iron or an alloycontaining one or more such metals and which may promote theinter-bonding of diamond grains. The sintering aid may also be referredto as a catalyst material for diamond and a binder material. Intersticeswithin the sintered PCD material may be wholly or partially filled withresidual catalyst material. PCD may be formed on a substrate, such as acobalt-cemented tungsten carbide substrate, which may provide a sourceof cobalt catalyst material for the PCD.

PCD material may be used as an abrasive compact in a wide variety oftools for cutting, machining, milling, grinding, drilling or degradinghard or abrasive materials such as rock, metal, ceramics, composites andwood-containing materials. For example, tool inserts comprising PCDmaterial are widely used within drill bits used for boring into theearth in the oil and gas drilling industry.

In many of these applications, the temperature of the PCD material maybecome elevated as it engages rock or other workpieces or bodies.Mechanical properties of PCD material such as abrasion resistance,hardness and strength tend to deteriorate at elevated temperatures,which may be promoted by the residual catalyst material within the bodyof PCD material.

It is desirable to improve the abrasion resistance of a body of PCDmaterial when used as an abrasive compact in tools such as thosementioned above, as this allows extended use of the cutter, drill ormachine in which the abrasive compact is located. This is typicallyachieved by manipulating variables such as average diamondparticle/grain size, overall binder content, particle density and thelike.

For example, it is well known in the art to increase the abrasionresistance of an ultrahard composite by reducing the overall grain sizeof the component ultrahard particles. Typically, however, as thesematerials are made more wear resistant they become more brittle or proneto fracture.

Abrasive compacts designed for improved wear performance will thereforetend to have poor impact strength or reduced resistance to spalling.This trade-off between the properties of impact resistance and wearresistance makes designing optimised abrasive compact structures,particularly for demanding applications, inherently self-limiting.

Additionally, because finer grained structures will typically containmore solvent/catalyst or metal binder, they tend to exhibit reducedthermal stability when compared to coarser grained structures. Thisreduction in optimal behaviour for finer grained structures can causesubstantial problems in practical applications where the increased wearresistance is nonetheless required for optimal performance.

Prior art methods to solve this problem have typically involvedattempting to achieve a compromise by combining the properties of bothfiner and coarser ultrahard particle grades in various manners withinthe ultrahard abrasive layer.

Another conventional solution is to remove, typically by acid leaching,the catalyst/solvent or binder phase from the PCD material.

It is typically extremely difficult and time consuming to remove thebulk of a metallic catalyst/solvent effectively from a PCD table,particularly from the thicker PCD tables required by currentapplications. Achieving appreciable leaching depths can take so long asto be commercially unfeasible or require undesirable interventions suchas extreme acid treatment or physical drilling of the PCD tables.

The development of an abrasive compact that can achieve improvedproperties of impact and fatigue resistance consistent with coarsergrained materials, whilst still retaining good wear resistance andreduced incidence of cracking is highly desirable.

SUMMARY

Viewed from a first aspect there is provided a polycrystalline diamondconstruction comprising a body of polycrystalline diamond materialformed of:

-   -   a mass of diamond grains exhibiting inter-granular bonding and        defining a plurality of interstitial regions therebetween, and    -   a non-diamond phase at least partially filling a plurality of        the interstitial regions to form non-diamond phase pools, the        non-diamond phase pools each having an individual        cross-sectional area,    -   wherein the percentage of non-diamond phase in the total area of        a cross-section of the body of polycrystalline diamond material        is between around 0 to 5%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in an        analysed image of a cross-section through the body of        polycrystalline material is less than around 0.7 microns squared        when analysed using an image analysis technique at a        magnification of around 1000 and an image area of 1280 by 960        pixels.

Viewed from a second aspect there is provided a polycrystalline diamondconstruction comprising a body of polycrystalline diamond materialformed of:

-   -   a mass of diamond grains exhibiting inter-granular bonding and        defining a plurality of interstitial regions therebetween, and    -   a non-diamond phase at least partially filling a plurality of        the interstitial regions to form non-diamond phase pools, the        non-diamond phase pools each having an individual        cross-sectional area,    -   wherein the percentage of non-diamond phase in the total area of        a cross-section of the body of polycrystalline diamond material        is between around 5 to 10%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in an        analysed image of a cross-section through the body of        polycrystalline diamond material is less than around 0.340        microns squared when analysed using an image analysis technique        at a magnification of around 1000 and an image area of 1280 by        960 pixels.

Viewed from a third aspect there is provided a polycrystalline diamondconstruction comprising a body of polycrystalline diamond materialformed of:

-   -   a mass of diamond grains exhibiting inter-granular bonding and        defining a plurality of interstitial regions therebetween, and    -   a non-diamond phase at least partially filling a plurality of        the interstitial regions to form non-diamond phase pools, the        non-diamond phase pools each having an individual        cross-sectional area,    -   wherein the percentage of non-diamond phase in the total area of        a cross-section of the polycrystalline diamond construction is        between around 10 to 15%, and    -   the mean of the individual cross-sectional areas of the        non-diamond phase pools in an analysed image of a cross section        through the body of polycrystalline material is less than around        0.340 microns squared when analysed using an image analysis        technique at a magnification of around 3000 and an image area of        1280 by 960 pixels.

Viewed from a fourth aspect there is provided a polycrystalline diamondconstruction comprising a body of polycrystalline diamond materialformed of:

-   -   a mass of diamond grains exhibiting inter-granular bonding and        defining a plurality of interstitial regions therebetween, and    -   a non-diamond phase at least partially filling a plurality of        the interstitial regions to form non-diamond phase pools, the        non-diamond phase pools each having an individual        cross-sectional area,    -   wherein the percentage of non-diamond phase in the total area of        a cross-section of the polycrystalline diamond construction is        between around 15 to 30%, and    -   the mean of the individual cross-sectional areas of the        non-diamond phase pools in an analysed image of a cross section        through the body of polycrystalline material is between around        0.005 to 0.340 microns squared when analysed using an image        analysis technique at a magnification of around 10000 and an        image area of 1280 by 960 pixels.

In some embodiments, the body of polycrystalline diamond material has alargest dimension of around 6 mm or greater.

In some embodiments, the body of polycrystalline diamond material has athickness of around 0.3 mm or greater.

Viewed from a fifth aspect there is provided a method for making apolycrystalline diamond construction, the method comprising:

-   -   providing a mass of diamond grains having a first average size;    -   arranging the mass of diamond grains to form a pre-sinter        assembly with a body of material for forming a substrate; and    -   treating the pre-sinter assembly in the presence of a catalyst        material for diamond at an ultra-high pressure of around 7 GPa        or greater and a temperature at which diamond is more        thermodynamically stable than graphite to sinter together the        diamond grains and a substrate bonded thereto along an interface        to form an integral PCD construction; the diamond grains        exhibiting inter-granular bonding and defining a plurality of        interstitial regions therebetween, a non-diamond phase at least        partially filling a plurality of the interstitial regions to        form non-diamond phase pools, the non-diamond phase pools each        having an individual cross-sectional area,    -   wherein the percentage of non-diamond phase in the total area of        a cross-section of the body of polycrystalline diamond material        is between around 0 to 5%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in the        image analysed is less than around 0.7 microns squared when        analysed using an image analysis technique at a magnification of        around 1000 and an image area of 1280 by 960 pixels; or    -   the percentage of non-diamond phase in the total area of a        cross-section of the body of polycrystalline diamond material is        between around 5 to 10%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in the        image analysed is less than around 0.340 microns squared when        analysed using an image analysis technique at a magnification of        around 1000 and an image area of 1280 by 960 pixels; or    -   the percentage of non-diamond phase in the total area of a        cross-section of the polycrystalline diamond construction is        between around 10 to 15%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in the        image analysed is less than around 0.340 microns squared when        analysed using an image analysis technique at a magnification of        around 3000 and an image area of 1280 by 960 pixels; or    -   the percentage of non-diamond phase in the total area of a        cross-section of the polycrystalline diamond construction is        between around 15 to 30%, and the mean of the individual        cross-sectional areas of the non-diamond phase pools in the        image analysed is between around 0.005 to 0.340 microns squared        when analysed using an image analysis technique at a        magnification of around 10000 and an image area of 1280 by 960        pixels.

BRIEF DESCRIPTION OF DRAWINGS

Non-limiting embodiments will now be described by way of example andwith reference to the accompanying drawings in which:

FIG. 1 is a schematic drawing of the microstructure of a body of PCDmaterial;

FIG. 2 is a schematic drawing of a PCD compact comprising a PCDstructure bonded to a substrate;

FIG. 3 is a schematic side view of an example assembly comprising firstand second structures;

FIG. 4 is a schematic diagram of part of an example pressure andtemperature cycle for making a super-hard construction;

FIGS. 5 to 9 are schematic diagrams of parts of example pressure andtemperature cycles for making a PCD construction; and

FIGS. 10 a and 10 b are processed images of a micrograph of a polishedsection of an embodiment of a body of PCD material at different diamonddensities.

DETAILED DESCRIPTION

As used herein, “polycrystalline diamond” (PCD) material comprises amass of diamond grains, a substantial portion of which are directlyinter-bonded with each other and in which the content of diamond is atleast about 80 volume percent of the material. In one embodiment of PCDmaterial, interstices between the diamond gains may be at least partlyfilled with a binder material comprising a catalyst for diamond. As usedherein, “interstices” or “interstitial regions” are regions between thediamond grains of PCD material. In embodiments of PCD material,interstices or interstitial regions may be substantially or partiallyfilled with a material other than diamond, or they may be substantiallyempty. Embodiments of PCD material may comprise at least a region fromwhich catalyst material has been removed from the interstices, leavinginterstitial voids between the diamond grains.

As used herein, a “PCD structure” comprises a body of PCD material.

As used herein, a “metallic” material is understood to comprise a metalin unalloyed or alloyed form and which has characteristic properties ofa metal, such as high electrical conductivity.

As used herein, “catalyst material” for diamond, which may also bereferred to as solvent/catalyst material for diamond, means a materialthat is capable of promoting the growth of diamond or the directdiamond-to-diamond inter-growth between diamond grains at a pressure andtemperature condition at which diamond is thermodynamically stable.

A filler or binder material is understood to mean a material that whollyor partially fills pores, interstices or interstitial regions within apolycrystalline structure.

A multi-modal size distribution of a mass of grains is understood tomean that the grains have a size distribution with more than one peak,each peak corresponding to a respective “mode”. Multimodalpolycrystalline bodies may be made by providing more than one source ofa plurality of grains, each source comprising grains having asubstantially different average size, and blending together the grainsor particles from the sources. In one embodiment, the PCD structure maycomprise diamond grains having a multimodal distribution.

As used herein, the term ‘total binder area’ is expressed as thepercentage of non-diamond phase(s) in the total cross-sectional area ofa polished cross section of the body of PCD material being analysed.

With reference to FIG. 1, a body of PCD material 10 comprises a mass ofdirectly inter-bonded diamond grains 12 and interstices 14 between thediamond grains 12, which may be at least partly filled with filler orbinder material.

FIG. 2 shows an embodiment of a PCD composite compact 20 for use as acutter comprising a body of PCD material 22 integrally bonded at aninterface 24 to a substrate 30. The substrate 30 may be formed of, forexample, cemented carbide material and may be, for example, cementedtungsten carbide, cemented tantalum carbide, cemented titanium carbide,cemented molybdenum carbide or mixtures thereof. The binder metal forsuch carbides may be, for example, nickel, cobalt, iron or an alloycontaining one or more of these metals. Typically, this binder will bepresent in an amount of 10 to 20 mass %, but this may be as low as 6mass % or less. Some of the binder metal may infiltrate the body ofpolycrystalline diamond material 22 during formation of the compact 20.

An example of a method for producing the PCD compact 20 comprising thebody of PCD material 22, as shown in FIGS. 1 and 2, is now describedwith reference to FIGS. 3 to 9. As shown in FIG. 3, a PCD structure (thesecond structure) 200 is disposed adjacent a cemented carbide substrate(the first structure) 300, a thin layer or film 400 of binder materialcomprising Co connecting opposite major surfaces of the PCD structure200 and the substrate 300 to comprise an assembly encased in a housing100 for an ultra-high pressure, high temperature press (not shown). TheCTE of the PCD material comprised in the PCD structure 200 is in therange from about 2.5×10-6 per degree Celsius to about 4×10-6 per degreeCelsius and the CTE of the cobalt-cemented tungsten carbide materialcomprised in the substrate 300 is in the range from about 5.4×10-6 perdegree Celsius to about 6×10-6 per degree Celsius (the CTE values arefor 25 degrees Celsius). In this example, the substrate 300 and the PCDstructure 200 contain binder material comprising Co. It is estimatedthat PCD material would have a Young's modulus from about 900gigapascals to about 1,400 gigapascals depending on the grade of PCD andthat the substrate would have a Young's modulus from about 500gigapascals to about 650 gigapascals depending largely on the contentand composition of the binder material.

FIG. 4 shows a schematic phase diagram of carbon in terms of pressure pand temperature T axes, showing the line D-G of thermodynamicequilibrium between diamond and graphite allotropes, diamond being themore thermally stable in region D and graphite being the more thermallystable in region G of the diagram. The line S-L shows schematically thetemperature at which the binder material melts or solidifies at variouspressures, this temperature tending to increase with increasingpressure. Note that this temperature is likely to be different from thatfor the binder material in a pure form because the presence of carbonfrom the diamond and or some dissolved WC is expected to reduce thistemperature, since the presence of carbon in solution is expected toreduce the melting point of cobalt and other metals. The assemblydescribed with reference to FIG. 3 may be under a first pressure P1 ofabout 7.5 gigapascals to about 8 gigapascal and at a temperature ofabout 1,450 degrees Celsius to about 1,800 degrees Celsius, at acondition at which the PCD material has been formed by sintering anaggregation of diamond grains disposed adjacent the substrate. There maybe no substantial interruption between the formation of the PCD in situat the sinter pressure and sinter temperature on the one hand andsubjecting the assembly to the first pressure P1 on the other; it is thesubsequent relationship between the reduction of the pressure and thetemperature at stages I and II that is the more relevant aspect of themethod. At the sinter temperature, the Co binder material will be moltenand expected to promote the direct inter-growth sintering of the diamondgrains to form the PCD material, the diamond comprised in the PCDmaterial being thermodynamically substantially more stable than graphiteat the sinter temperature and sinter pressure.

With further reference to FIG. 4, the pressure and temperature of theassembly may be reduced to ambient levels in stages I, II and III. In aparticular example, the pressure may be reduced in stage I from thefirst pressure P1 to a second pressure P2 of about 5.5 gigapascals toabout 6 gigapascals while reducing the temperature to about 1,350degrees Celsius to about 1,500 degrees Celsius to ensure that thepressure-temperature condition remains such that diamond is morethermodynamically stable than graphite and that the binder materialremains substantially molten. In stage II, the temperature may then bereduced to about 1,100 degrees Celsius to a temperature in the range ofabout 1,200 degrees Celsius while maintaining the pressure above theline D-G in the diamond-stable region D to solidify the binder material;and in stage III the pressure and temperature may be reduced to ambientlevels in various ways. The PCD construction can then be removed fromthe press apparatus. Note that the stages I, II and III are used merelyto explain FIG. 4 and there may not be clear distinction between thesestages in practice. For example these stages may flow smoothly into oneanother with no substantial period of maintaining pressure andtemperature conditions at the end of a stage. Alternatively, some or allof the stages may be distinct and the pressure and temperature conditionat the end of a stage may be maintained for a period.

In some examples, a pre-sinter assembly for making a PCD or PCBNconstruction, for example, may be prepared and provided in situ at thefirst pressure P1 as follows. A cup may be provided into which anaggregation comprising a plurality of diamond or CBN grains and asubstrate may be assembled, the interior shape of the cup beinggenerally that of the desired shape of the PCD or PCBN structure (havingregard to likely distortion during the sintering step). The aggregationmay comprise substantially loose diamond or CBN grains or diamond- orCBN-containing pre-cursor structures such as granules, discs, wafers orsheets. The aggregation may also include catalyst material for diamond,matrix material for PCBN, or pre-cursor material for catalyst or matrixmaterial, which may be admixed with the diamond or CBN grains and ordeposited on the surfaces of the diamond or CBN grains. The diamond orCBN grains may have a mean size of at least about 0.1 micron and or atmost about 75 microns and may be substantially mono-modal ormulti-modal. The aggregation may also contain additives for reducingabnormal diamond or CBN grain growth or the aggregation may besubstantially free of catalyst material or additives. Alternatively oradditionally, another source of catalyst or matrix material such ascobalt may be provided, such as the binder material in a cementedcarbide substrate. A sufficient quantity of the aggregation may beplaced into the cup and then the substrate may inserted into the cupwith a proximate end pushed against the aggregation. The pre-sinterassembly comprising the aggregation and the substrate may be encasedwithin a metal jacket comprising the cup, subjected to a heat treatmentto burn off organic binder that may be comprised in the aggregation, andencapsulated within a housing (which may be referred to as a capsule)suitable for an ultra-high pressure press. The housing may be placed ina suitable ultra-high pressure press apparatus and subjected to a sinterpressure and sinter temperature to form the assembly comprising a PCD orPCBN structure adjacent the substrate, connected by a thin film ofmolten binder comprising cobalt. In examples such as these, the sinterpressure may be regarded as the first pressure P1.

In an example arrangement, a pre-sinter assembly for making a PCD orPCBN construction may be prepared and provided in a press apparatus atthe first pressure P1 as follows. A PCD or PCBN structure may beprovided pre-sintered in a previous ultra-high pressure, hightemperature process. The PCD or PCBN structure may contain binder ormatrix material comprising cobalt, located in interstitial regionsbetween the diamond or CBN grains comprised in the PCD or PCBN material.In the case of PCD material, the PCD structure may have at least aregion substantially free of binder material. For example, the PCDstructure may have been treated in acid to remove binder material fromthe interstices at least adjacent a surface of the PCD structure orthroughout substantially the entire volume of the PCD structure (orvariations between these possibilities), leaving at least a region thatmay contain pores or voids. In some examples, voids thus created may befilled with a filler material that may or may not comprise bindermaterial. The PCD or PCBN structure may be placed against a substrateand the resulting pre-construction assembly may be encased within ahousing suitable for an ultra-high pressure press. The housing may beplaced in a suitable ultra-high pressure press apparatus and thesubjected to the first pressure P1 at a temperature at which the bindermaterial is in the liquid state (at a condition in region D of FIG. 4).

Example methods for making an example PCD construction will be describedbelow with reference to FIGS. 5 to 9. In each figure, only part of thepressure and temperature cycle is shown, the part beginning atrespective first pressures P1, at which the PCD material comprised inthe construction becomes formed by sintering, and ending after thetemperature has been reduced sufficiently to solidify the bindermaterial and the pressure has been reduced from the second pressure P2.

In some examples, a pre-sinter assembly may be provided, comprising anaggregation of a plurality of diamond grains located adjacent a surfaceof a substrate comprising cobalt-cemented tungsten carbide. The diamondgrains may have a mean size in the range of about 0.1 to about 40microns. The pre-sinter assembly may be encapsulated within a capsulefor an ultra-high pressure press apparatus, into which the capsule maybe loaded. The capsule may be pressurised at ambient temperature to apressure of at least about 6.5 gigapascals and heated to a temperaturein the range of about 1,500 to about 1,600 degrees Celsius,substantially greater than the melting point (at the pressure) of thecobalt-based binder material comprised in the substrate and causing thecobalt material to melt. At this temperature the pre-sinter assembly maybe at a first pressure P1 in the range from about 7.5 to about 10gigapascals (P1 may be somewhat higher than 7 gigapascals at leastpartly as a result of the increase in temperature). The first pressureP1 and the temperature may be substantially maintained for at leastabout 1 minute, or in any event sufficiently long to sinter together thediamond grains (in these examples, the sinter pressure will besubstantially P1). The pressure may then be reduced from first pressureP1 through a second pressure P2 in the range from about 5.5 to about 8.5gigapascals. The second pressure may be the pressure at which the bindermaterial begins to solidify as the temperature is reduced through itssolidification temperature.

The temperature of the pre-sinter assembly may be reduced simultaneouslywith pressure, provided that it remains greater than the temperature atwhich the cobalt-based binder material will have completely solidified.As the pressure is reduced from P2, the temperature may also be reducedthrough the solidification line of the cobalt-based binder material,resulting in the solidification of the binder material. In theseparticular examples, the pressure is substantially continuously reducedfrom the first pressure P1, through the second pressure P2 and throughthe pressure(s) at which the binder material solidifies, withoutsubstantial pause. The rate of reduction of the pressure and ortemperature may be varied or the rate of the reduction of either or bothmay be substantially constant, at least until the cobalt-based bindermaterial has solidified. The temperature may also be reducedsubstantially continuously at least until it is sufficiently low forsubstantially all the cobalt-based binder material to have solidified.The temperature and pressure may then be reduced to ambient conditions,the capsule removed from the ultra-high pressure press apparatus and theconstruction removed from the capsule. The construction may comprise asintered PCD structure formed joined to the substrate, the PCD structurehaving become joined to the substrate in the same general step in whichthe PCD material was formed by the sintering together of the pluralityof diamond grains. A thin layer rich in cobalt will be present betweenthe PCD structure and the substrate, joining together these structures.

In a particular example method illustrated in FIG. 5, the first pressureP1 is about 7.6 gigapascals, the temperature at the first pressure beingin the range of about 1,500 to about 1,600 degrees Celsius, and anexample second pressure P2 is about 6.8 gigapascals.

In a particular example method illustrated in FIG. 6, the first pressureP1 is about 7.7 gigapascals, the temperature at the first pressure beingin the range of about 1,500 to about 1,600 degrees Celsius, and anexample second pressure P2 is about 6.9 gigapascals.

In a particular example method illustrated in FIG. 7, the first pressureP1 is about 7.8 gigapascals, the temperature at the first pressure beingin the range of about 1,500 to about 1,600 degrees Celsius, and anexample second pressure P2 is about 6.9 gigapascals.

In a particular example method illustrated in FIG. 8, the first pressureP1 is about 7.9 gigapascals, the temperature at the first pressure beingin the range of about 1,500 to about 1,600 degrees Celsius, and anexample second pressure P2 is about 5.5 gigapascals.

In the example method illustrated in FIG. 9, the first pressure P1 isabout 9.9 gigapascals, the temperature at the first pressure being about2,000 degrees Celsius, and an example second pressure P2 may be about8.1 gigapascals.

Note that the line S-L in FIGS. 5 to 9, indicating the melting andsolidification temperatures of cobalt-based binder material in thepresence of carbon, was estimated based on a calculation using availabledata. In practice, it may be advisable not to rely completely oncalculated values lying on S-L but to carry out trial and errorexperiments to discover the melting and solidification temperatures forthe particular binder material and pressure being used.

The method used to measure the pressure and temperature cycles asillustrated in FIGS. 5 to 9 is measured using so-called K-typethermocouples and knowledge of the melting temperatures of copper (Cu)and silver (Ag). Data for the melting points of Cu and Ag measured usingK-type thermocouples up at 60 kilobars was published by P. W. Mirwaldand G. C. Kennedy in an article entitled “The melting curve of gold,silver and copper to 60-Kbar pressure—a reinvestigation”, published on10 Nov. 1979 in the Journal of Geophysical Research volume 84, numberB12, pages 6750 to 6756, by The American Geophysical Union. A K-typethermocouple may also be referred to as a “chromel-alumel” thermocouple,in which the “chromel” component comprises 90 percent nickel and 10percent chromium, and the “alumel” component comprises 95 percentnickel, 2 percent manganese, 2 percent aluminium and 1 percent silicon.The method includes inserting the junction of a first K-typethermocouple into a body consisting essentially of Cu and the junctionof a second K-type thermocouple into a body consisting essentially ofAg, and positioning the two bodies proximate the pre-sinter assemblywithin the capsule. The readings from both thermocouples are recordedthroughout at least a part of the pressure and temperature cycle and thereadings processed and converted to pressure and temperature valuesaccording to the published data.

In some examples, the construction may comprise a polycrystalline cubicboron nitride (PCBN) structure joined to a cobalt cemented carbidesubstrate. In some example methods, an aggregation comprising cubicboron nitride (CBN) grains may be provided. The CBN grains may have amean size of at least about 0.1 micron and at most about 30 microns. Theaggregation may comprise tungsten carbide grains and or pre-cursormaterial for forming a matrix within which the CBN grains can dispersedin sintered PCBN material. In some examples, the aggregation maycomprise a mixture of cubic boron nitride powder with a binder materialcontaining Ti, Al, W or Co and the mixture cast into sheets using aplasticizer material. In some examples, the super-hard structure maycomprise PCBN material substantially as described in internationalapplication number WO2007049140 and may be manufactured by a methodincluding providing a powdered composition suitable for the manufactureof PCBN, the powder comprising at least 80 volume percent CBN particlesand a powdered binder material, and subjecting the powder composition toattrition milling. The composition may comprise CBN particles of morethan one average particle size. In various examples, the average size ofthe CBN particles may be at most about 12 microns or at most 2 microns.The binder material may include one or more of phase(s) containingaluminium, silicon, cobalt, molybdenum, tantalum, niobium, nickel,titanium, chromium, tungsten, yttrium, carbon and iron. The bindermaterial may include powder with uniform solid solution of more than oneof aluminium, silicon, cobalt, nickel, titanium, chromium, tungsten,yttrium, molybdenum, niobium, tantalum, carbon and iron.

Various kinds of ultra-high pressure presses may be used, includingbelt-type, tetrahedral multi-anvil, cubic multi-anvil, walker-type ortorroidal presses. The choice of press type is likely to depend on thevolume of the super-hard construction to be made and the pressure andtemperature desired for sintering the super-hard material. For example,tetrahedral and cubic presses may be suitable for sintering commerciallyviable volumes of PCD and PCBN material at pressures of at least about 7gigapascals or at least about 7.7 gigapascals.

Some example methods may include subjecting a PCD or PCBN constructionto a heat treatment at a temperature of at least about 500 degreesCelsius, at least about 600 degrees Celsius or at least about 650degrees Celsius for at least about 5 minutes, at least about 15 minutesor at least about 30 minutes. In some embodiments, the temperature maybe at most about 850 degrees Celsius, at most about 800 degrees Celsiusor at most about 750 degrees Celsius. In some embodiments, the PCDstructure may be subjected to the heat treatment for at most about 120minutes or at most about 60 minutes. In one embodiment, the PCD or PCBNstructure may be subjected to the heat treatment in a vacuum. Forexample, U.S. Pat. No. 6,517,902 discloses a form of heat treatment forpre-form elements having a facing table of PCD bonded to a substrate ofcemented tungsten carbide with a cobalt binder. The substrate includesan interface zone with at least 30 percent by volume of the cobaltbinder in a hexagonal close packed crystal structure.

While wishing not to be bound by a particular theory, the method mayresult in a reduced likelihood or frequency of cracking of super-hardconstructions because the residual stress within the construction isreduced.

Non-limiting examples are described in more detail below.

Example 1

A PCD insert for a rock-boring drill bit was made as described below.

A pre-sinter assembly was prepared, comprising an aggregation of aplurality of diamond grains disposed against a proximate end of agenerally cylindrical cemented carbide substrate. The aggregationcomprised a plurality of wafers comprising diamond grains dispersedwithin an organic binder material, the diamond grains having a mean sizeof at least about 15 microns and at most about 30 microns. The substratecomprised about 90 weight percent WC grains cemented together by abinder material comprising Co. The pre-sinter assembly was enclosed in ametal jacket and heated to burn off the organic binder comprised in thewafers, and the jacketed, pre-sinter assembly was encapsulated in acapsule for an ultra-high pressure, high temperature multi-anvil pressapparatus.

The pre-sinter assembly was subjected to a pressure of about 7.7gigapascals and a temperature of about 1,550 degrees Celsius to sinterthe diamond grains directly to each other to form a layer of PCDmaterial connected to the proximate end of the substrate by a film ofmolten binder material comprising cobalt from the substrate. Thepressure was reduced to about 5.5 gigapascals and the temperature wasreduced to about 1,450 degrees Celsius, maintaining conditions at whichthe diamond comprised in the PCD is thermodynamically stable (inrelation to graphite, a softer allotrope of carbon) and at which thebinder material is in the liquid phase. The temperature was then reducedto about 1,000 degrees Celsius to solidify the binder material and forma construction comprising the layer of PCD bonded to the substrate bythe solidified binder material, and the pressure and temperature werethen reduced to ambient conditions.

The construction was subjected to a heat treatment at 660 degreesCelsius for about 2 hours at substantially ambient pressure in asubstantially non-oxidising atmosphere, and then cooled to ambienttemperature. No cracks were evident in the PCD layer after the heattreatment.

The construction was processed by grinding and polishing to provide aninsert for a rock-boring drill bit.

For comparison, a reference construction was made as follows. Apre-sinter assembly was prepared as described above in relation to theexample pre-sinter assembly. The pre-sinter assembly was subjected to apressure of about 7.7 gigapascal and a temperature of about 1,550degrees Celsius to sinter the diamond grains directly to each other toform a layer of PCD material connected to the proximate end of thesubstrate by a film of molten binder material comprising cobalt from thesubstrate. The temperature was reduced to about 1,000 degrees Celsius tosolidify the binder material and form a construction comprising thelayer of PCD bonded to the substrate by the solidified binder material,and then the pressure and temperature were reduced to ambientconditions. The construction was subjected to a heat treatment at 660degrees Celsius for about 2 hours at substantially ambient pressure in asubstantially non-oxidising atmosphere, and then cooled to ambienttemperature. Severe cracks were evident at the side of the PCD layerafter the heat treatment.

Example 2

A PCD insert for a rock-boring drill bit was made as described below.

A pre-sinter assembly was prepared, comprising a PCD structure having agenerally disc-like shape disposed against a proximate end of agenerally cylindrical cemented carbide substrate. PCD structure had beenmade in a previous step involving sintering together an aggregation of aplurality of diamond grains at an ultra-high pressure of less than about7 gigapascals and a high temperature (at which the diamond wasthermodynamically more stable than graphite). The substrate comprisedabout 90 weight percent WC grains cemented together by a binder materialcomprising Co. The pre-sinter assembly was enclosed in a metal jacketand heated to burn off the organic binder comprised in the wafers, andthe jacketed, pre-sinter assembly was encapsulated in a capsule for anultra-high pressure, high temperature multi-anvil press apparatus.

The pre-sinter assembly was subjected to a pressure of about 7.7gigapascals and a temperature of about 1,550 degrees Celsius to modifythe microstructure of the PCD structure. The pressure was reduced toabout 5.5 gigapascals and the temperature was reduced to about 1,450degrees Celsius, maintaining conditions at which the diamond comprisedin the PCD is thermodynamically stable (in relation to graphite, asofter allotrope of carbon) and at which the binder material is in theliquid phase. The temperature was then reduced to about 1,000 degreesCelsius to solidify the binder material and form a constructioncomprising the layer of PCD bonded to the substrate by the solidifiedbinder material, and the pressure and temperature were then reduced toambient conditions.

The construction was subjected to a heat treatment at 660 degreesCelsius for about 2 hours at substantially ambient pressure in asubstantially non-oxidising atmosphere, and then cooled to ambienttemperature. No cracks were evident in the PCD layer after the heattreatment.

The construction was processed by grinding and polishing to provide aninsert for a rock-boring drill bit.

Certain terms and concepts as used herein will be briefly explained

As used herein, “super-hard” means a Vickers hardness of at least 25gigapascal. Synthetic and natural diamond, polycrystalline diamond(PCD), cubic boron nitride (cBN) and polycrystalline cBN (PCBN) materialare examples of super-hard materials. Synthetic diamond, which is alsocalled man-made diamond, is diamond material that has been manufactured.

As used herein, PCBN material comprises grains of cubic boron nitride(cBN) dispersed within a matrix comprising metal and or ceramicmaterial.

PCD material comprises a mass (an aggregation of a plurality) of diamondgrains, a substantial portion of which are directly inter-bonded witheach other and in which the content of diamond is at least about 80volume percent of the material. Interstices between the diamond grainsmay be at least partly filled with a binder material comprising acatalyst material for synthetic diamond, or they may be substantiallyempty. Catalyst material (which may also be referred to assolvent/catalyst material, reflecting the understanding that thematerial may perform a catalytic and or solvent function in promotingthe growth of diamond grains and the sintering of diamond grains) forsynthetic diamond is capable of promoting the growth of syntheticdiamond grains and or the direct inter-growth of synthetic or naturaldiamond grains at a temperature and pressure at which synthetic ornatural diamond is thermodynamically more stable than graphite. Examplesof catalyst materials for diamond are Fe, Ni, Co and Mn, and certainalloys including these. Bodies comprising PCD material may comprise atleast a region from which catalyst material has been removed from theinterstices, leaving interstitial voids between the diamond grains.Various grades of PCD material may be made. As used herein, a PCD gradeis a variant of PCD material characterised in terms of the volumecontent and size of diamond grains, the volume content of interstitialregions between the diamond grains and composition of material that maybe present within the interstitial regions. Different PCD grades mayhave different microstructure and different mechanical properties, suchas elastic (or Young's) modulus E, modulus of elasticity, transverserupture strength (TRS), toughness (such as so-called K1C toughness),hardness, density and coefficient of thermal expansion (CTE). DifferentPCD grades may also perform differently in use. For example, the wearrate and fracture resistance of different PCD grades may be different.

Thermally stable PCD material comprises at least a part or volume ofwhich exhibits no substantial structural degradation or deterioration ofhardness or abrasion resistance after exposure to a temperature aboveabout 400 degrees Celsius, or even above about 700 degrees Celsius. Forexample, PCD material containing less than about 2 weight percent ofcatalyst metal for diamond such as Co, Fe, Ni, Mn in catalyticallyactive form (e.g. in elemental form) may be thermally stable. PCDmaterial that is substantially free of catalyst material incatalytically active form is an example of thermally stable PCD. PCDmaterial in which the interstices are substantially voids or at leastpartly filled with ceramic material such as SiC or salt material such ascarbonate compounds may be thermally stable, for example. PCD structureshaving at least a significant region from which catalyst material fordiamond has been depleted, or in which catalyst material is in a formthat is relatively less active as a catalyst, may be described asthermally stable PCD.

Other examples of superhard materials include certain compositematerials comprising diamond or cBN grains held together by a matrixcomprising ceramic material, such as silicon carbide (SiC), or cementedcarbide material, such as Co-bonded WC material (for example, asdescribed in U.S. Pat. Nos. 5,453,105 or 6,919,040). For example,certain SiC-bonded diamond materials may comprise at least about 30volume percent diamond grains dispersed in a SiC matrix (which maycontain a minor amount of Si in a form other than SiC). Examples ofSiC-bonded diamond materials are described in U.S. Pat. Nos. 7,008,672;6,709,747; 6,179,886; 6,447,852; and International Applicationpublication number WO2009/013713).

Young's modulus is a type of elastic modulus and is a measure of theuni-axial strain in response to a uni-axial stress, within the range ofstress for which the material behaves elastically. A method of measuringthe Young's modulus E is by means of measuring the transverse andlongitudinal components of the speed of sound through the material usingultrasonic waves.

As used herein, the thickness of the PCD structure 22, 200 or thesubstrate 30, 300, or some part of the PCD structure or the substrate isthe thickness measured substantially perpendicularly to the interface24. In some embodiments, the PCD structure, or body of PCD material 22,200 may have a generally wafer, disc or disc-like shape, or be in thegeneral form of a layer. In some embodiments, the PCD structure 22, 200may have a thickness of at least about 0.3 mm, at least about 0.5 mm, atleast about 0.7 mm, at least about 1 mm, at least about 1.3 mm or atleast about 2 mm. In one embodiment, the PCD structure 22, 200 may havea thickness in the range from about 2 mm to about 3 mm.

In some embodiments, the substrate 30, 300 may have the general shape ofa wafer, disc or post, and may be generally cylindrical in shape. Thesubstrate 30, 300 may have, for example, an axial thickness at leastequal to or greater than the axial thickness of the body of PCD material22, 200, and may be for example at least about 1 mm, at least about 2.5mm, at least about 3 mm, at least about 5 mm or even at least about 10mm in thickness. In one embodiment, the substrate 30, 300 may have athickness of at least 2 cm.

The PCD structure 22, 200 may be joined to the substrate 30, 300 forexample only on one side thereof, the opposite side of the PCD structurenot being bonded to the substrate 30, 300.

In some embodiments, the largest dimension of the body of PCD material22, 200 is around 6 mm or greater, for example in embodiments where thebody of PCD material is cylindrical in shape, the diameter of the bodyis around 6 mm or greater.

In some versions of the method, prior to sintering, the aggregated massof diamond particles/grains may be disposed against the surface of thesubstrate generally in the form of a layer having a thickness of leastabout 0.6 mm, at least about 1 mm, at least about 1.5 mm or even atleast about 2 mm. The thickness of the mass of diamond grains may reducesignificantly when the grains are sintered at an ultra-high pressure.

The ultrahard particles used in the present process may be of natural orsynthetic origin. The mixture of ultrahard particles may be multimodal,that it is may comprise a mixture of fractions of diamond particles orgrains that differ from one another discernibly in their averageparticle size. Typically the number of fractions may be:

-   -   a specific case of two fractions    -   three or more fractions.

By “average particle/grain size” it is meant that the individualparticles/grains have a range of sizes with the mean particle/grain sizerepresenting the “average”. Hence the major amount of theparticles/grains will be close to the average size, although there willbe a limited number of particles/grains above and below the specifiedsize. The peak in the distribution of the particles will therefore be atthe specified size. The size distribution for each ultrahardparticle/grain size fraction is typically itself monomodal, but may incertain circumstances be multimodal. In the sintered compact, the term“average particle grain size” is to be interpreted in a similar manner.

As shown in FIG. 1, the bodies of polycrystalline diamond materialproduced by an embodiment additionally have a binder phase present. Thisbinder material is preferably a catalyst/solvent for the ultrahardabrasive particles used. Catalyst/solvents for diamond are well known inthe art. In the case of diamond, the binder is preferably cobalt,nickel, iron or an alloy containing one or more of these metals. Thisbinder may be introduced either by infiltration into the mass ofabrasive particles during the sintering treatment, or in particulateform as a mixture within the mass of abrasive particles. Infiltrationmay occur from either a supplied shim or layer of the binder metal orfrom the carbide support. Typically a combination of the admixing andinfiltration approaches is used.

During the high pressure, high temperature treatment, thecatalyst/solvent material melts and migrates through the compact layer,acting as a catalyst/solvent and causing the ultrahard particles to bondto one another. Once manufactured, the PCD construction thereforecomprises a coherent matrix of ultrahard (diamond) particles bonded toone another, thereby forming an ultrahard polycrystalline compositematerial with many interstices or pools containing binder material asdescribed above. In essence, the final PCD construction thereforecomprises a two-phase composite, where the ultrahard abrasive diamondmaterial comprises one phase and the binder (non-diamond phase), theother.

In one form, the ultrahard phase, which is typically diamond,constitutes between 80% and 95% by volume and the solvent/catalystmaterial the other 5% to 20%.

The relative distribution of the binder phase, and the number of voidsor pools filled with this phase, is largely defined by the size andshape of the diamond grains.

The binder (non-diamond) phase can help to improve the impact resistanceof the more brittle abrasive phase, but as the binder phase typicallyrepresents a far weaker and less abrasion resistant fraction of thestructure, high quantities will tend to adversely affect wearresistance. Additionally, where the binder phase is also an activesolvent/catalyst material, its increased presence in the structure cancompromise the thermal stability of the compact.

FIGS. 10 a and 10 b are an example of a processed SEM image of apolished section of a PCD material, for a diamond intensity of 0 (FIG.10 a) and a diamond intensity of 15 (FIG. 10 b) showing the boundariesbetween diamond grains. These boundary lines were provided by imageanalysis software and were used to measure the total non-diamond phase(eg binder) surface area in a cross-section through the body of PCDmaterial and surface area of the individual non-diamond phase(interstitial) regions which are indicated as dark areas. Thecross-section through the body of PCD material may be at any orientationthrough the body of PCD material for the following analysis to beconducted and results to be achieved. The image analysis technique isdescribed in more detail below.

As a non-limiting example, the cross section shown in FIGS. 10 a and 10b may be exposed for viewing by cutting a section of the PCD compositecompact by means of a wire EDM. The cross section may be polished inpreparation for viewing by a microscope, such as a scanning electronmicroscope (SEM) and a series of micrographic images of the type shownin FIGS. 5 a and 5 b may be taken. Each of the images may be analysed bymeans of image analysis software to determine the total binder area andindividual binder areas between the diamond grains. The values of thetotal binder area and individual binder area are determined byconducting a statistical evaluation on a large number of collectedimages taken on the scanning electron microscope.

The magnification selected for the microstructural analysis has asignificant effect on the accuracy of the data obtained. Imaging atlower magnifications offers an opportunity to sample, representatively,larger particles or features in a microstructure but may tend tounder-represent smaller particles or features as they are notnecessarily sufficiently resolved at that magnification. By contrast,higher magnifications allow resolution and hence detailed measurement offine-scale features but can tend to sample larger features such thatthey intersect the boundaries of the images and hence are not adequatelymeasured. It has been appreciated that it is therefore important toselect an appropriate magnification for any quantitative microstructuralanalysis technique. The appropriateness is therefore determined by thesize of the features that are being characterised. The magnificationsselected for the various measurements described herein are discussed inmore detail below.

Unless otherwise stated herein, dimensions of total binder area andindividual binder area within the body of PCD material refer to thedimensions as measured on a surface of, or a section through, a bodycomprising PCD material and no stereographic correction has beenapplied. For example, the measurements are made by means of imageanalysis carried out on a polished surface, and a Saltykov correctionhas not been applied in the data stated herein.

In measuring the mean value of a quantity or other statistical parametermeasured by means of image analysis, several images of different partsof a surface or section (hereinafter referred to as samples) are used toenhance the reliability and accuracy of the statistics. The number ofimages used to measure a given quantity or parameter may be, for examplebetween 10 to 30. If the analysed sample is uniform, which is the casefor PCD, depending on magnification, 10 to 20 images may be consideredto represent that sample sufficiently well.

The resolution of the images needs to be sufficiently high for theinter-grain and inter-phase boundaries to be clearly made out and, forthe measurements stated herein an image area of 1280 by 960 pixels wasused.

In the statistical analysis, 15 images were taken of different areas ona surface of a body comprising the PCD material, and statisticalanalysis was carried out on each image.

Images used for the image analysis were obtained by means of scanningelectron micrographs (SEM) taken using a backscattered electron signal.The back-scatter mode was chosen so as to provide high contrast based ondifferent atomic numbers and to reduce sensitivity to surface damage (ascompared with the secondary electron imaging mode).

A number of factors have been identified as being important for imagecapturing. These are:

-   -   SEM Voltage which, for the purposes of the measurements stated        herein remained constant and was around 15 kV;    -   working distance which also remained constant and was around 8        mm    -   image sharpness    -   sample polishing quality,    -   image contrast levels which were selected to provide clear        separation of the microstructural features;    -   magnification (should be varied according to different diamond        grain size and is as stated below),    -   number of images taken.

Given the above conditions, the image analysis software used was able toseparate distinguishably the diamond and binder phases and theback-scatter images were taken at approximately 45° to the edge of thesamples.

The magnification used in the image analysis should be selected in sucha way that the feature of interest is adequately resolved and describedby the available number of pixels. In PCD image analysis variousfeatures of different size and distribution are measured simultaneouslyand it is not practical to use a separate magnification for each featureof interest.

It is difficult to identify the optimum magnification for each featuremeasurement in the absence of a reference measurement result. It couldvary from one operator to another. Therefore, a procedure is proposedfor the selection of the magnification.

The size of a statistically significant number of diamond grains in themicrostructure is measured and the average value taken.

As used herein in relation to grains or particles and unless otherwisestated or implied, the term “size” refers to the length of the grainviewed from the side or in cross section using image analysistechniques.

The number of pixels that describe this average length is determined anda range of pixel values are established to fix the magnification.

In the image analysis technique, the original image was converted to agreyscale image. The image contrast level was set by ensuring thediamond peak intensity in the grey scale histogram image occurredbetween 15 and 20. As mentioned above, several images of different partsof a surface or section were taken to enhance the reliability andaccuracy of the statistics. For measurements of total non-diamond phase(eg binder) area, the greater the number of images, the more accuratethe results are perceived to be. For example, about 15000 measurementswere taken, 1000 per image with 15 images.

The steps taken by the image analysis programme may be summarised ingeneral as follows:

-   1. The original image was converted to a greyscale image. The image    contrast level was set by ensuring the diamond peak intensity in the    grey scale histogram image occurred between 10 and 20.-   2. An auto threshold feature was used to binarise the image and    specifically to obtain clear resolution of the diamond and binder    phases.-   3. The binder was the primary phase of interest in the current    analysis.-   4. The software, having the trade name analySIS Pro from Soft    Imaging System® GmbH (a trademark of Olympus Soft Imaging Solutions    GmbH) was used and excluded from the analysis any particles which    touched the boundaries of the image. This required appropriate    choice of the image magnification:-   a. If too low then resolution of fine particles is reduced.-   b. If too high then:-   i. Efficiency of coarse grain separation is reduced.-   ii. High numbers of coarse grains are cut by the boarders of the    image and hence less of these grains are analysed.-   iii. Thus more images must be analysed to get a    statistically-meaningful result.-   5. Each particle was finally represented by the number of continuous    pixels of which it is formed.-   6. The AnalySIS software programme proceeded to detect and analyse    each particle in the image. This can be automatically repeated for    several images.-   7. A large number of outputs was available. The outputs may be    post-processed further, for example using statistical analysis    software and/or carrying out further feature analysis, for example    the analysis described below for determining the mean of the total    binder area for all images and the means of the individual binder    areas.

If appropriate thresholding is used, the image analysis technique isunlikely to introduce further errors in measurements which would have apractical effect on the accuracy of those measurements, with theexception of small errors related to the rounding of numbers. In thecurrent analysis, the statistical mean values of the total binder areaand individual binder areas were used as, according to the CentralLimitation Theorem, the distribution of an average tends to be normal asthe sample size increases, regardless of the distribution from which theaverage is taken except when the moments of the parent distribution donot exist. All practical distributions in statistical engineering havedefined moments, and thus the Central Limitation Theorem applies in thepresent case. It was therefore deemed appropriate to use the statisticalmean values.

The individual non-diamond (eg binder or catalyst/solvent) phase areasor pools, which are easily distinguishable from that of the ultrahardphase using electron microscopy, were identified using theabove-mentioned standard image analysis tools. The total non-diamondphase areas (in square microns) in the analysed cross-sectional imageswere determined by summing the individual binder pool areas within theentire microstructural image area that was analysed.

The collected distributions of this data were then evaluatedstatistically and an arithmetic average was then determined. Hence themean total binder pool area in the surface of the microstructure beinganalysed was calculated

It is anticipated that microstructural parameters may alter slightlyfrom one area of an abrasive compact to another, depending on formationconditions. Hence the microstructural imaging is carried out so as torepresentatively sample the bulk of the ultrahard composite portion ofthe compact.

Additional non-limiting examples are now described. Three sets ofsamples were produced as follows: a multimodal (trimodal) diamond powdermix with average diamond grain size of approximately 13 μm and 1 weightpercent cobalt admix was prepared, in sufficient quantity to provideapproximately 2 g admix per sample. The admix for each sample was thenpoured into or otherwise arranged in a Niobium inner cup. A cementedcarbide substrate of approximately 13 weight percent cobalt content andhaving a non-planar interface was placed in each inner cup on the powdermix. A titanium cup was placed in turn over this structure and theassembly sealed to produce a canister. The canisters were pre-treated byvacuum outgassing at approximately 1050° C., and divided into three setswhich were sintered at three distinct ultrahigh pressure and temperatureconditions in the diamond-stable region, namely at approximately 5.5 GPa(Set 1), 6.8 GPa (Set 2), and 7.7 GPa (Set 3). Specifically thecanisters were sintered at temperatures sufficient to melt the cobalt soas to produce PCD constructions with well-sintered PCD tables andwell-bonded substrates. The technique described above in connection withFIGS. 3 to 9 was applied for the sintering of the canisters at 7.7 GPa(set 3). The resulting superhard constructions were not subjected to anypost-synthesis leaching treatment.

Image analysis was then conducted on each of these superhardconstructions using the techniques described above and in particular thedetermination of appropriate magnification described above to determinethe mean total binder area in a polished cross-section and meancross-sectional binder area for each sample.

The experiments may be repeated for different diamond grain sizecompositions and the results are set out in Table 1.

TABLE 1 Grain Binder Size Total Binder Area microns Area %micron{circumflex over ( )}2 Magnification Mean StdDev 0.01 13.46002.2750 8.0699 0.4446 1000x 12.5755 3.1707 8.0223 0.2802 1000x 10.88001.8440 6.4004 0.2638 1000x  3.9700 0.7990 10.3135 0.1528 3000x

It was determined from the above experiments that, for a totalnon-diamond phase area (for example binder area) in the range of around0 to 5%, it is possible to achieve an associated individual non-diamondarea of less than around 0.7 micon², as determined using an imageanalysis technique applying a magnification of around 1000 and analysingan image area of 1280×960 pixels, with the largest dimension of the bodyof PCD material being around 6 mm or greater. The thickness of the bodyof PCD material in these embodiments may be, for example, around 0.3 mmor greater.

Furthermore, for a total non-diamond phase area (for example binderarea) in the range of around 5 to 10%, it is possible to achieve anassociated cross-sectional individual non-diamond phase area of lessthan around 0.340 micon², as determined using an image analysistechnique applying a magnification of between around 1000 and analysingan image area of 1280×960 pixels, with the largest dimension of the bodyof PCD material being around 6 mm or greater. The thickness of the bodyof PCD material in these embodiments may be, for example, around 0.3 mmor greater.

Also, for a total non-diamond phase area (for example binder area) inthe range of around 10 to 15%, it is possible to achieve an associatedcross-sectional individual non-diamond phase area of less than around0.340 micon², as determined using an image analysis technique applying amagnification of between around 3000 and analysing an image area of1280×960 pixels, with the largest dimension of the body of PCD materialbeing around 6 mm or greater. The thickness of the body of PCD materialin these embodiments may be, for example, around 0.3 mm or greater.

Also, for a total non-diamond phase area (for example binder area) inthe range of around 15 to 30%, it is possible to achieve an associatedcross-sectional individual non-diamond phase area in the range of around0.005 to around 0.340 micon², as determined using an image analysistechnique applying a magnification of between around 10000 and analysingan image area of 1280×960 pixels, with the largest dimension of the bodyof PCD material being around 6 mm or greater. The thickness of the bodyof PCD material in these embodiments may be, for example, around 0.3 mmor greater.

Whilst not wishing to be bound by a particular theory, using theconditions described herein it was determined possible to achieve totalbinder areas in the ranges specified above together with theabove-mentioned ranges of associated individual binder areas. These havebeen determined to assist generating a more wear-resistant body of PCDmaterial which, when used as a cutter, may significantly enhance thedurability of the cutter produced according to some embodimentsdescribed herein.

In addition, various arrangements and combinations are envisaged for themethod by the disclosure, and examples of the method may further includeone or more of the following non-exhaustive and non-limiting aspects invarious combinations.

There may be provided a method for making a super-hard constructioncomprising:

a first structure joined to a second structure, the first structurecomprising first material having a first coefficient of thermalexpansion (CTE) and a first Young's modulus, and the second structurecomprising second material having a second CTE and a second Young'smodulus; the first CTE and the second CTE being substantially differentfrom each other and the first Young's modulus and the second Young'smodulus being substantially different from each other; at least one ofthe first or second materials comprising super-hard material; the methodincluding:forming an assembly comprising the first material, the second materialand a binder material arranged to be capable of bonding the first andsecond materials together, the binder material comprising metal;subjecting the assembly to a sufficiently high temperature for thebinder material to be in the liquid state and to a first pressure atwhich the super-hard material is thermodynamically stable; reducing thepressure to a second pressure at which the super-hard material isthermodynamically stable, the temperature being maintained sufficientlyhigh to maintain the binder material in the liquid state; reducing thetemperature to solidify the binder material; and reducing the pressureand the temperature to an ambient condition to provide the super-hardconstruction.

In some embodiments, the CTE of one of the first or second materials isat least about 2.5×10-6 per degree Celsius and at most about 5.0×10-6per degree Celsius and the CTE of the other of the first or secondmaterials is at least about 3.5×10-6 per degree Celsius and at mostabout 6.5×10-6 per degree Celsius, at about 25 degrees Celsius.

In some embodiments, the Young's modulus of one of the first or secondmaterials is at least about 500 gigapascals and at most about 1,300gigapascals and the Young's modulus of the other of the first and secondmaterials is at least about 800 gigapascals and at most about 1,600gigapascals.

The Young's moduli of the first and second materials may, for example,differ by at least about 10%.

In some embodiments, the CTE of the first and second materials may, forexample, differ by at least about 10%.

The method may further include sintering an aggregation of a pluralityof grains of the super-hard material in the presence of sinter catalystmaterial at a sinter pressure and a sinter temperature to form thesecond structure.

The method may include disposing an aggregation of grains of super-hardmaterial adjacent the first structure and in the presence of the bindermaterial to form a pre-sinter assembly; subjecting the pre-sinterassembly to a sinter pressure and a sinter temperature to melt thebinder material and sinter the grains of super-hard materials and formthe second structure comprising polycrystalline super-hard materialconnected to the first structure by the binder material in the moltenstate.

In some embodiments, the first pressure is substantially the sinterpressure.

The method may further include providing the first structure, providingthe second structure comprising polycrystalline super-hard material,disposing the first structure adjacent the second structure and forminga pre-construction assembly, and applying a pressure to thepre-construction assembly, increasing the pressure from ambient pressureto the first pressure.

The method may, for example, include subjecting an aggregation of aplurality of grains of super-hard material to a sinter pressure and asinter temperature at which the super-hard material is capable of beingsintered to form the second material, and reducing the pressure andtemperature to an ambient condition to provide the second structure; thefirst pressure being substantially greater then the sinter pressure.

The second structure may comprise diamond material and the bindermaterial comprises catalyst material for diamond.

The first and second structures may each comprise diamond material andthe binder material comprises catalyst material for diamond.

In some embodiments, the difference between the second pressure and thefirst pressure is at least about 0.5 gigapascal.

The method may further include subjecting the super-hard construction tofurther heat treatment at a treatment temperature and a treatmentpressure at which the super-hard material is thermodynamicallymeta-stable.

The super-hard material may comprise diamond material and the treatmenttemperature is at least about 500 degrees Celsius and the treatmentpressure is less than about 1 gigapascal.

The method may include the step of reducing the pressure from the firstpressure to an intermediate pressure for an holding period, and thenfurther reducing the pressure from the intermediate pressure to thesecond pressure.

The first pressure may, for example, be at least about 7 gigapascal, theintermediate pressure may be, for example, at least about 5.5gigapascals and less than about 10 gigapascals, the holding period may,for example, be at least about 1 minute and the second pressure may, forexample, be at least about 5.5 gigapascals and at most about 7gigapascals.

The pressure at which the binder material begins to solidify responsiveto the reduction in temperature may, for example, be substantially equalto the second pressure in some embodiments.

In other embodiments, the pressure at which the binder material beginsto solidify responsive to the reduction in temperature may besubstantially less than the second pressure.

In some embodiments, the first structure comprises cobalt-cementedtungsten carbide material and the second material comprises PCDmaterial, the CTE of the cemented carbide material being in the range ofabout 4.5×10-6 to about 6.5×10-6 per degree Celsius, the CTE of the PCDmaterial being in the range of about 3.0×10-6 to about 5.0×10-6 perdegree Celsius; the Young's modulus of the cemented carbide materialbeing in the range of about 500 to about 1,000 gigapascals, and theYoung's modulus of the PCD material being in the range of about 800 toabout 1,600 gigapascals; the first pressure being in the range of about6 to about 10 gigapascals, and the second pressure being in the range ofabout 5.5 to about 8 gigapascals.

In some embodiments, the pressure at which the cobalt-based bindermaterial comprised in the cemented carbide material begins to solidifyis equal to the second pressure.

The second pressure may, for example, be in the range of about 6.5 toabout 7.5 gigapascals.

In some embodiments, the second structure comprises PCD material and themethod includes subjecting the super-hard construction to further heattreatment for a treatment period in the range of about 30 to about 90minutes at a treatment temperature in the range of about 550 to about650 degrees Celsius.

The method may include processing the super-hard construction to providea tool element. The super-hard construction may be suitable for aninsert for a rock-boring drill bit, for an impact tool for degradingrock or pavement or for a machine tool.

Disclosed methods have the aspect of reducing the likelihood orfrequency of cracking of super-hard constructions, particularly whensubjected to heating in subsequent manufacturing steps or to elevatedtemperatures in use.

1. A polycrystalline diamond construction comprising a body ofpolycrystalline diamond material formed of: a mass of diamond grainsexhibiting inter-granular bonding and defining a plurality ofinterstitial regions therebetween, and a non-diamond phase at leastpartially filling a plurality of the interstitial regions to formnon-diamond phase pools, the non-diamond phase pools each having anindividual cross-sectional area, wherein the percentage of non-diamondphase in the total area of a cross-section of the body ofpolycrystalline diamond material is between around 0 to 5%, and the meanof the individual cross-sectional areas of the non-diamond phase poolsin an analysed image of a cross-section through the body ofpolycrystalline material is less than around 0.7 microns squared whenanalysed using an image analysis technique at a magnification of around1000 and an image area of 1280 by 960 pixels.
 2. A polycrystallinediamond construction comprising a body of polycrystalline diamondmaterial formed of: a mass of diamond grains exhibiting inter-granularbonding and defining a plurality of interstitial regions therebetween,and a non-diamond phase at least partially filling a plurality of theinterstitial regions to form non-diamond phase pools, the non-diamondphase pools each having an individual cross-sectional area, wherein thepercentage of non-diamond phase in the total area of a cross-section ofthe body of polycrystalline diamond material is between around 5 to 10%,and the mean of the individual cross-sectional areas of the non-diamondphase pools in an analysed image of a cross-section through the body ofpolycrystalline diamond material is less than around 0.340 micronssquared when analysed using an image analysis technique at amagnification of around 1000 and an image area of 1280 by 960 pixels. 3.A polycrystalline diamond construction comprising a body ofpolycrystalline diamond material formed of: a mass of diamond grainsexhibiting inter-granular bonding and defining a plurality ofinterstitial regions therebetween, and a non-diamond phase at leastpartially filling a plurality of the interstitial regions to formnon-diamond phase pools, the non-diamond phase pools each having anindividual cross-sectional area, wherein the percentage of non-diamondphase in the total area of a cross-section of the polycrystallinediamond construction is between around 10 to 15%, and the mean of theindividual cross-sectional areas of the non-diamond phase pools in ananalysed image of a cross section through the body of polycrystallinematerial is less than around 0.340 microns squared when analysed usingan image analysis technique at a magnification of around 3000 and animage area of 1280 by 960 pixels.
 4. A polycrystalline diamondconstruction comprising a body of polycrystalline diamond materialformed of: a mass of diamond grains exhibiting inter-granular bondingand defining a plurality of interstitial regions therebetween, and anon-diamond phase at least partially filling a plurality of theinterstitial regions to form non-diamond phase pools, the non-diamondphase pools each having an individual cross-sectional area, wherein thepercentage of non-diamond phase in the total area of a cross-section ofthe polycrystalline diamond construction is between around 15 to 30%,and the mean of the individual cross-sectional areas of the non-diamondphase pools in an analysed image of a cross section through the body ofpolycrystalline material is between around 0.005 to 0.340 micronssquared when analysed using an image analysis technique at amagnification of around 10000 and an image area of 1280 by 960 pixels.5. A polycrystalline diamond construction according to any one of thepreceding claims, wherein the body of polycrystalline diamond materialhas a largest dimension of around 6 mm or greater.
 6. A polycrystallinediamond construction according to any one of the preceding claims,wherein the body of polycrystalline diamond material has a thickness ofaround 0.3 mm or greater.
 7. The polycrystalline diamond constructionaccording to any one of the preceding claims, further comprising asubstrate bonded to the body of polycrystalline diamond material alongan interface.
 8. The polycrystalline diamond construction according toclaim 7, wherein the interface between the substrate and the body ofpolycrystalline diamond material is substantially non-planar.
 9. Thepolycrystalline diamond construction according to any one of claims 7 or8, wherein the substrate comprises cemented carbide.
 10. Thepolycrystalline diamond construction according to any one of claims 7 to9, wherein the substrate has a thickness at least equal to or greaterthan the thickness of the body of polycrystalline diamond material. 11.A cutter for boring into the earth comprising the polycrystallinediamond construction according to any one of the preceding claims.
 12. APCD element for a rotary shear bit for boring into the earth, for apercussion drill bit or for a pick for mining or asphalt degradation,comprising the polycrystalline diamond construction of any one of claims1 to
 10. 13. A drill bit or a component of a drill bit for boring intothe earth, comprising a polycrystalline superhard construction accordingto any one of claims 1 to
 10. 14. A method for making a polycrystallinediamond construction, the method comprising: providing a mass of diamondgrains having a first average size; arranging the mass of diamond grainsto form a pre-sinter assembly with a body of material for forming asubstrate; and treating the pre-sinter assembly in the presence of acatalyst material for diamond at an ultra-high pressure of around 7 GPaor greater and a temperature at which diamond is more thermodynamicallystable than graphite to sinter together the diamond grains and asubstrate bonded thereto along an interface to form an integral PCDconstruction; the diamond grains exhibiting inter-granular bonding anddefining a plurality of interstitial regions therebetween, a non-diamondphase at least partially filling a plurality of the interstitial regionsto form non-diamond phase pools, the non-diamond phase pools each havingan individual cross-sectional area, wherein the percentage ofnon-diamond phase in the total area of a cross-section of the body ofpolycrystalline diamond material is between around 0 to 5%, and the meanof the individual cross-sectional areas of the non-diamond phase poolsin the image analysed is less than around 0.7 microns squared whenanalysed using an image analysis technique at a magnification of around1000 and an image area of 1280 by 960 pixels; or the percentage ofnon-diamond phase in the total area of a cross-section of the body ofpolycrystalline diamond material is between around 5 to 10%, and themean of the individual cross-sectional areas of the non-diamond phasepools in the image analysed is less than around 0.340 microns squaredwhen analysed using an image analysis technique at a magnification ofaround 1000 and an image area of 1280 by 960 pixels; or the percentageof non-diamond phase in the total area of a cross-section of thepolycrystalline diamond construction is between around 10 to 15%, andthe mean of the individual cross-sectional areas of the non-diamondphase pools in the image analysed is less than around 0.340 micronssquared when analysed using an image analysis technique at amagnification of around 3000 and an image area of 1280 by 960 pixels; orthe percentage of non-diamond phase in the total area of a cross-sectionof the polycrystalline diamond construction is between around 15 to 30%,and the mean of the individual cross-sectional areas of the non-diamondphase pools in the image analysed is between around 0.005 to 0.340microns squared when analysed using an image analysis technique at amagnification of around 10000 and an image area of 1280 by 960 pixels.15. A method of forming the polycrystalline diamond construction of anyone of claims 1 to
 10. 16. A polycrystalline diamond constructionsubstantially as hereinbefore described with reference to any oneembodiment as that embodiment is illustrated in FIGS. 3 to 10 b of theaccompanying drawings.
 17. A method of forming the polycrystallinediamond construction substantially as hereinbefore described withreference to any one embodiment as that embodiment is illustrated inFIGS. 3 to 10 b of the accompanying drawings.